A sudden stop of the compressor or, conversely, continuous operation of the refrigerator without shutting down most often indicates a failure of the thermostat. This small device, often called thermal relay or a thermostat, is responsible for maintaining the set temperature inside the chambers. When it breaks, food begins to deteriorate or freeze into an ice block, which requires immediate intervention.
The main difficulty that home craftsmen face is not the dismantling process itself, but in finding a suitable replacement. Original spare parts may be discontinued, unavailable in stores in your city, or be unreasonably expensive. Fortunately, in most cases thermostat can be replaced with a universal analogue or part from another manufacturer, if you know the key parameters.
In this article we will look at how to choose the right analogue, what to look for when marking and how to avoid fatal errors during installation. You will learn how the contacts differ NO and NC, why the temperature range is important and how to carry out diagnostics with a multimeter before purchasing a new part.
Diagnostics and signs of a thermostat malfunction
Before looking for a replacement, you need to make sure that the problem lies in the thermostat. Often the symptoms of a breakdown of this unit are confused with a malfunction of the compressor start relay or a freon leak. If the refrigerator hums, but does not cool, or freezes so much that the door warps from ice, it is worth checking thermal sensor.
Primary diagnostics can be carried out visually and by ear. When the set temperature is reached, the compressor should click and stop. If this does not happen for a long time, and the temperature inside the chamber is significantly below normal, most likely the contacts inside the relay are “stuck” in the closed state.
For an accurate check, you will need a multimeter. It is necessary to get to the mounting location of the thermostat, usually it is located inside the refrigerator compartment or in a niche above the compressor, and ring the contacts. Depending on the type of relay, at room temperature the circuit can be either closed or open.
- 🔍 No click: The compressor operates continuously, without responding to turning the temperature control knob.
- ❄️ Increasing snow: A thick ice crust forms on the back wall of the refrigerator compartment ("fur coat").
- 🔌 Complete silence: The refrigerator does not turn on at all, although the light inside is on and there is voltage in the socket.
⚠️ Attention: Before carrying out any diagnostic work and Before replacing, be sure to disconnect the refrigerator from the power supply. Working with electrical appliances under voltage is deadly and can lead to a short circuit.
If the continuity test shows an open circuit where there should be a contact, or a short circuit where there should be insulation, the part requires replacement. However, even with working electrical parts, the mechanical part (bellows tube) could lose its seal, which would also require the installation of a new element.
Key parameters for selecting an analogue
The search for a replacement begins with studying the markings on the body of the old device. Refrigerator manufacturers rarely produce thermal relays on their own; most often they purchase them from specialized factories, such as Klixon, Danfoss (Danfoss), Orbital or Ranco. Therefore, you need to search not by the brand of the refrigerator, but by the codes on the relay itself.
The most important parameter is the temperature range. Three values will be indicated on the case: switch-on temperature, switch-off temperature and maximum temperature. For example, the marking may state that the relay opens the circuit at -14°C and closes at -12°C. If you set an analogue with other parameters, the refrigerator will either freeze poorly or work without interruption.
It is also critically important to pay attention to the length capillary tube. This is a thin copper wire that is inserted into the evaporator or attached to the outside of it. If the tube is too short, you simply will not be able to reach the attachment point without extension, which will break the tightness of the system. If it is too long, you will have to carefully lay it, avoiding kinks.
Another nuance is the type of contacts. They can be normally closed (open when cooled) or normally open (closed when heated). For refrigerators, normally closed contacts are mainly used, but for two-chamber models with separate circuits, other options may also be found.
Compatibility table and popular analogues
Many thermostats have direct cross-analogs. Below is a table that will help you navigate the replacement of popular models. However, remember that the characteristics may vary slightly depending on the batch and year of manufacture.
| Original (Marking) | Possible analogue | Application | Features |
|---|---|---|---|
| TAM-118, TAM-125, TAM-133 | K-50, K-59 (Danfoss) | Single chamber refrigerators | Universal replacement, tube adjustment required |
| T-110, T-111, T-112 | K-57, K-58 (Danfoss) | Two-chamber (refrigerator compartment) | Wider temperature range |
| 17M6001 (Orbital) | K-59 L1958 | Modern models | High accuracy, long tube |
| 2925 (Danfoss) | K-50 P1968 | Freezers | Low temperature mode |
When using the table, keep in mind that universal thermostats often require adjustment. A locking screw can be installed on the stem, which locks the range of adjustment with a handle on the body. It is better not to change its position without special equipment, since it is very easy to reset the factory calibration.
If you do not find an exact match in the catalogs, you can use a thermostat with a wider temperature range, but be sure to check the switch-off point. It should not be higher than that of the original, otherwise the products will defrost.
Instructions for replacing the thermostat with your own hands
The process of replacing the thermostat is technically simple, but requires care. The main task is not to damage the capillary tube and to connect the electrical contacts correctly. Any error can lead to the new thermostat immediately failing or not working correctly.
First you need to remove the old regulator. To do this, remove the temperature control knob (sometimes there is a locking screw under it), unscrew the fixing screws of the relay housing and carefully remove the bellows tube from the mounting hole in the chamber wall or disconnect the sensor from the evaporator.
☑️ Checklist before installation
Installing a new thermal relay done in reverse order. Insert the sensing tube into the same hole at the same depth as the old one. If the tube is longer, it can be carefully twisted into a ring with a diameter of at least 4-5 cm and secured in free space, avoiding sharp corners.
Pay special attention to connecting the wires. Before disconnecting the old relay, be sure to take a photo of the circuit or mark the wires with a marker. In older models, the color marking may not correspond to modern standards, so you need to rely on the connection diagram printed on the case or in the instructions.
⚠️ Attention: The capillary tube is filled with gas or liquid under pressure. Never bend it at a 90-degree angle or allow it to be struck. Damage to the tube makes the thermostat unusable.
After connecting, assemble the housing, install the regulator knob and turn on the refrigerator. The initial work cycle may take several hours. At this time, do not open the doors frequently so that the thermostat can be correctly calibrated and make the first on-off cycle.
Replacement specifics in two-chamber models
In two-chamber refrigerators, the thermoregulation system is more complex. Here, either one common thermostat can be used to control the compressor, or two separate ones: one for the refrigerator compartment, the other for the freezer (in models with No Frost or two compressors). An error in choosing the type of relay will lead to disruption of the entire system.
If your refrigerator has one compressor and one capillary tube goes into the freezer, and the sensor is in the refrigerator compartment, then when replacing it is important to use a relay with the correct “on” characteristic. It should turn on the compressor when it becomes too warm in the upper chamber, even if it is still cold in the freezer.
Why can’t you install a relay from a single-chamber refrigerator to a two-chamber one?
Thermostats for single-chamber models have too low a switch-on temperature (about -10...-12°C). In a two-chamber refrigerator, this will cause the food in the upper compartment to defrost, since the compressor will turn on too late.
For models with a system No Frost electronic sensors (thermistors) are often used rather than mechanical relays. Replacing them requires not only physical installation, but sometimes also reflashing the controller or adjusting the resistances if the refrigerator model does not automatically recognize the new sensor.
It is also important to check the insulation condition of the wires passing through the chamber. At low temperatures, the insulation hardens and cracks, which can cause a short circuit. When replacing a thermal relay, it is recommended, if possible, to replace the wiring section inside the chamber with a frost-resistant cable.
Frequent errors and troubleshooting
Even with the correct selection of spare parts, installation may fail due to minor nuances. One of the most common mistakes is incorrect seating depth of the capillary tube. If it enters the evaporator too deeply or too shallowly, the thermostat will “lie” about the real temperature inside the chamber.
Another problem is poor contact in the terminal block. If the screws are loosely tightened, the contact at the connection point will begin to heat up, the metal will oxidize, and as a result, the thermal relay will burn out, and along with it, the wiring of the refrigerator may suffer. Use a high-quality screwdriver and check the tightness.
- 🌡️ Incorrect range: Installing a relay with a shutdown temperature higher than the required one will lead to defrosting of the products.
- 🔧 Mechanical damage: Accidental cutting of the tube during installation requires a complete replacement of the unit.
- ⚡ Mixed wires: Can cause the fan to work instead of the compressor or vice versa.
⚠️ Attention: Technical specifications of refrigerators and availability of spare parts may change by manufacturers. Before ordering a specific thermal relay model, check the current catalog numbers on the official website of the manufacturer of your equipment or in specialized spare parts stores.
If after replacement the refrigerator begins to work cyclically, but the cycles are too short (it turns on and off often), it is possible that a relay was selected with a temperature differential that is too narrow. In this case, you will need to replace it again with an analogue with other parameters.
Questions and answers (FAQ)
Is it possible to repair a thermal relay rather than changing it?
Theoretically, you can try to disassemble mechanical thermostats and clean the contacts, but in practice this rarely gives long-term results result. Improper calibration of springs and bellows will lead to unstable operation. It’s easier and more reliable to buy a new analogue, which is inexpensive.
What to do if the capillary tube of the new relay is shorter than the old one?
It is strictly forbidden to extend the copper tube of the thermorelay, since there is refrigerant inside under pressure. If the tube is short, you will have to mount the thermostat unit itself closer to the input point, which may require modifications to the housing or wiring.
How to understand that the thermostat is not suitable for the temperature?
If the refrigerator turns off when it is still warm in the chamber, or does not turn off, turning the food into ice, then the temperature range is selected incorrectly. Another sign may be the absence of a click when turning the control knob to the extreme positions.
Is it necessary to defrost the refrigerator before replacing?
Yes, complete defrosting is required. This will allow you to work safely with electricians, avoid water getting on the contacts and make it easier to remove the old capillary tube that could freeze to the walls of the evaporator.